Method for anodizing aluminum alloy workpiece, method for surface treating aluminum alloy workpiece, and anodizing solution mixes

ABSTRACT

A method for surface treating an aluminum alloy workpiece having zinc and magnesium includes: providing the aluminum alloy workpiece; polishing the aluminum alloy to achieve a mirror effect; degreasing the aluminum alloy workpiece; stripping a black film formed on the aluminum alloy workpiece; anodizing the aluminum alloy workpiece in an anodizing solution which includes acidic solution and an additive with a concentration of 0.5 mg/L to 25 g/L to form an oxidation film on the surface of the aluminum alloy workpiece, wherein the additive including at least one compound selected from a group consisting of adipic acid, 1,2,3-Benzotriazole, oxalic acid, sodium malate, and glycerin; and sealing the aluminum alloy workpiece. This disclosure further provides an anodizing solution applied in the method for surface treating an aluminum alloy workpiece and a method for anodizing the aluminum alloy workpiece using the same.

FIELD

The subject matter herein generally relates to a method for anodizingaluminum alloy workpiece, a method for surface treating aluminum alloyworkpiece, and anodizing solution mixes.

BACKGROUND

Aluminum alloy having zinc and magnesium is light, has low density, highstrength, and good heat dissipation, so it is widely used as housings ofelectronics. However, if the aluminum alloy having zinc and magnesium isanodized to acquire a mirror surface, intermetallic compounds, such asCu, Zn or MgZn2, may dissolved prior to the aluminum base, thus theremay be some bank marks and corrosion spots occurred on the surface ofthe aluminum alloy.

BRIEF DESCRIPTION OF THE DRAWINGS

Implementations of the present technology will now be described, by wayof example only, with reference to the attached figures.

FIG. 1 is a flowchart of an embodiment of a method for surface treatingan aluminum alloy workpiece.

FIG. 2 is a table showing steps and parameters of embodiment 1 throughembodiment 6 and comparative embodiment 1 through embodiment 6.

FIG. 3 is a table showing steps and parameters of embodiment 7 throughembodiment 9 and comparative embodiment 7.

FIG. 4 is a table showing test results of gloss and observation ofsurface topography of embodiment 1 through embodiment 9.

FIG. 5 is a table showing test results of gloss and observation ofsurface topography of comparative embodiment 1 through embodiment 4.

FIG. 6 is a table showing test results of gloss and observation ofsurface topography of comparative embodiment 5 through embodiment 7.

FIG. 7 is a microphotograph of the surface of the aluminum alloyworkpiece in embodiment 1.

FIG. 8 is a microphotograph of the surface of the aluminum alloyworkpiece in comparative embodiment 1.

FIG. 9 is a three dimensional surface topography photo of the aluminumalloy in embodiment 1.

FIG. 10 is a three dimensional surface topography photo of the aluminumalloy in comparative embodiment 1.

DETAILED DESCRIPTION

It will be appreciated that for simplicity and clarity of illustration,where appropriate, reference numerals have been repeated among thedifferent figures to indicate corresponding or analogous elements. Inaddition, numerous specific details are set forth in order to provide athorough understanding of the embodiments described herein. However, itwill be understood by those of ordinary skill in the art that theembodiments described herein can be practiced without these specificdetails. In other instances, methods, procedures and components have notbeen described in detail so as not to obscure the related relevantfeature being described. Also, the description is not to be consideredas limiting the scope of the embodiments described herein. The drawingsare not necessarily to scale and the proportions of certain parts may beexaggerated to better illustrate details and features of the presentdisclosure.

The present disclosure is relation to methods for surface treating andanodizing an aluminum alloy having zinc and magnesium, and anodizingsolution thereof.

Referring to FIG. 1, a flowchart of an example embodiment of a methodfor surface treating an aluminum alloy having zinc and magnesium whichbeing thus illustrated. The example method 100 is provided by way ofexample, as there are a variety of ways to carry out the method. Eachblock shown in FIG. 1 represents one or more processes, methods orsubroutines, carried out in the example method 100. Additionally, theillustrated order of blocks is by example only and the order of theblocks can change according to the present disclosure. The examplemethod 100 can begin at block 101.

At block 101, an aluminum alloy workpiece having zinc and magnesium canbe provided.

At block 102, the aluminum alloy workpiece can be polished to achieve abright, smooth mirror effect. In at least one embodiment, an surface ofthe aluminum alloy workpiece can be polished by chemical mechanicalpolishing, and the polishing step can include a sanding step and aprecision grinding step. A temperature of the sanding step can be in arange from about 23 degrees centigrade to about 30 degrees centigrade,and a period of the sanding step can be in a range from about 10 minutesto about 15 minutes. A temperature of the precision grinding step can bein a range from about 23 degrees centigrade to about 30 degreescentigrade, and a period of the precision grinding step can be in arange from about 10 minutes to about 15 minutes.

At block 103, the aluminum alloy workpiece can be degreased to removeoil from the surface thereof, and the surface of the aluminum alloyworkpiece can be hydrophilic. A period of the degreasing step can be ina range from about 3 minutes to about 5 minutes, and a temperature ofthe degreasing step can be in a range from about 50 degrees centigradeto 60 degrees centigrade. A degreasing solution can include sodiumphosphate, and a mass concentration of the sodium hydroxide can be in arange from about 40 grams per liter (g/L) to about 70 grams per liter(g/L).

At block 104, a black layer formed after polishing can be stripped awayfrom the surface of the aluminum alloy workpiece by immersing thealuminum alloy workpiece into an acid solution. A temperature of thedegreasing step can be room temperature. A period can be in a range fromabout 20 seconds to about 120 seconds. The acid solution can be asulfuric acid solution, and a volume ratio of the sulfuric acid solutioncan be in a range from about 15 percent to about 35 percent.

At block 105, the aluminum alloy workpiece can be anodized by ananodizing treatment, such that an oxidation film is formed on thesurface of the aluminum alloy workpiece. The oxidation film can be aporous Al₂O₃ film having a plurality of micro-holes therein. A period ofthe anodizing step can be in a range from about 20 minutes to about 50minutes. A voltage of the anodizing step can be in a range from about 6volts to about 10 volts, and a temperature can be about 18 degreesCelsius to 26 degrees Celsius. An anodizing solution can include asulfuric acid solution with a mass concentration from about 150 g/L toabout 230 g/L and an additive with a mass concentration from about 0.5milligram per liter (mg/L) to about 25 g/L. The additive can include atleast one compound selected from a group consisting of adipic acid,1,2,3-Benzotriazole, oxalic acid, sodium malate and glycerin.

At block 106, the aluminum alloy workpiece can be sealed by a sealingtreatment in a sealing solution, such that the oxidation film can have agood wear resistance. A period of the sealing treatment can be in arange from about 15 minutes to about 20 minutes. A temperature of thesealing treatment can be in a range from about 90 degrees centigrade to95 degrees centigrade. A sealing solution can be a nickel acetatesolution with a mass concentration from about 5 g/L to about 10 g/L.

At block 107, the aluminum alloy workpiece can be dried by heating.

In other embodiments, between step 103 and step 107, there may be atleast one step for washing the aluminum alloy workpiece.

In other embodiments, the aluminum alloy workpiece can be polished byother methods, such as mechanical polishing, chemical polishing, orelectrolytic polishing. In other embodiments, the process at block 104can be omitted if there is no black layer formed on the surface of thealuminum alloy workpiece after mechanical polishing.

In other embodiments, the degreasing solution at block 103 can be acaustic soda solution, a sodium carbonate solution, a sodium silicatesolution, or a mixture solution. In other embodiments, the solution forstripping the black layer at block 104 can be a nitric acid solution orother solutions.

In other embodiments, the solution for anodizing at block 105 can beother acid solutions, such as a phosphoric acid solution, a chromic acidsolution, an oxalic acid solution, or a mixture solution of the abovesolutions. In other embodiments, the sealing solution can be nickelsulfate, nickel fluoride, or a mixture solution of the above solutions.

For further explanation, detailed embodiments and comparativeembodiments are described as follows.

Sixteen groups of aluminum alloy workpieces can be provided. Materialsof the aluminum alloy workpieces can be AZ91D type Al—Mg—Zn aluminumalloys. The first group through the ninth group of aluminum alloyworkpieces are treated by the method of the illustrated embodiment ofthis disclosure, serving and provided as embodiment 1 through embodiment9. The tenth group through the sixteenth group of the aluminum alloyworkpieces are treated by a method similar to the method of thisdisclosure, expect that the anodizing solution has no additive. Thetenth group through the sixteenth group of the aluminum alloy workpiecesare served and provided as comparative embodiment 1 through comparativeembodiment 7. FIG. 2 and FIG. 3 shows the steps and respectivecorresponding parameters (i.e., the period, temperature) of embodiments1-9 and comparative embodiment 1-7. The material ingredients and theconcentrations of the solutions of embodiment 1-9 are described asfollows. The material ingredients and the concentrations of thesolutions of comparative embodiment 1-7 can be similar with theembodiments 1-9 expect that anodizing solution has no additive.

Embodiment 1

The material ingredients and concentrations of the solutions are asfollows.

In the degreasing step: the mass concentration of the sodium phosphateis about 60 g/L.

In the black layer stripping step: the volume concentration of thesulfuric acid is about 20 percent.

In the anodizing step: the mass concentration of the sulfuric acid isabout 200 g/L, and the additive is oxalic acid with a mass concentrationof about 10 g/L.

In the sealing step: the mass concentration of the nickel acetate isabout 10 g/L.

Embodiment 2

The material ingredients and concentrations of the solutions are asfollows.

In the degreasing step: the mass concentration of the sodium phosphateis about 50 g/L.

In the black layer stripping step: the volume concentration of thesulfuric acid is about 15 percent.

In the anodizing step: the mass concentration of the sulfuric acidsolution is about 230 g/L, and the additive is adipic acid with a massconcentration of about 4 g/L.

In the sealing step: the mass concentration of the nickel acetate isabout 5 g/L.

Embodiment 3

The material ingredients and concentrations of the solutions are asfollows.

In the degreasing step: the mass concentration of the sodium phosphateis about 40 g/L.

In the black layer stripping step: the volume concentration of thesulfuric acid is about 25 percent.

In the anodizing step: the mass concentration of the sulfuric acidsolution is about 220 g/L, and the additive is 1,2,3-Benzotriazole witha mass concentration of about 4 g/L.

In the sealing step: the mass concentration of the nickel acetate isabout 10 g/L.

Embodiment 4

The material ingredients and concentrations of the solutions are asfollows.

In the degreasing step: the mass concentration of the sodium phosphateis about 70 g/L.

In the black layer stripping step: the volume concentration of thesulfuric acid solution is about 30 percent.

In the anodizing step: the mass concentration of the sulfuric acid isabout 190 g/L, and the additive is a mixture of oxalic acid and1,2,3-Benzotriazole. A mass concentration of the oxalic acid is about 10g/L, and a mass concentration of the 1,2,3-Benzotriazole is about 4 g/L.

In the sealing step: the mass concentration of the nickel acetate isabout 7 g/L.

Embodiment 5

The material ingredients and concentrations of the solutions are asfollows.

In the degreasing step: the mass concentration of the sodium phosphateis about 45 g/L.

In the black layer stripping step: the volume concentration of thesulfuric acid solution is about 23 percent.

In the anodizing step: the mass concentration of the sulfuric acidsolution can be 205 g/L, and the additive can be a mixture of oxalicacid and glycerin. A mass concentration of the oxalic acid is about 10g/L, and a mass concentration of the glycerin is about 10 g/L.

In the sealing step: the mass concentration of the nickel acetate isabout 8 g/L.

Embodiment 6

The material ingredients and concentrations of the solutions are asfollows.

In the degreasing step: the mass concentration of the sodium phosphateis about 48 g/L.

In the black layer stripping step: the volume concentration of thesulfuric acid solution is about 26 percent.

In the anodizing step: the mass concentration of the sulfuric acid isabout 180 g/L, and the additive can be a mixture of oxalic acid andsodium malate. A mass concentration of the oxalic acid is about 10 g/L,and a mass concentration of the sodium malate is about 5 g/L.

In the sealing step: the mass concentration of the nickel acetate can beabout 9 g/L.

Embodiment 7

The material ingredients and concentrations of the solutions are asfollows.

In the degreasing step: the mass concentration of the sodium phosphateis about 42 g/L.

In the black layer stripping step: the volume concentration of thesulfuric acid solution is about 35 percent.

In the anodizing step: the mass concentration of the sulfuric acid isabout 150 g/L, and the additive is a mixture of oxalic acid andglycerin. A mass concentration of the oxalic acid is about 10 g/L, and amass concentration of the glycerin is about 15 g/L.

In the sealing step: the mass concentration of the nickel acetate isabout 8 g/L.

Embodiment 8

The material ingredients and concentrations of the solutions are asfollows.

In the degreasing step: the mass concentration of the sodium phosphateis about 60 g/L.

In the black layer stripping step: the volume concentration of thesulfuric acid is about 20 percent.

In the anodizing step: the mass concentration of the sulfuric acidsolution is about 200 g/L, and the additive is oxalic acid with a massconcentration of about 5 g/L.

In the sealing step: the mass concentration of the nickel acetate isabout 8 g/L.

Embodiment 9

The material ingredients and concentrations of the solutions are asfollows.

In the degreasing step: the mass concentration of the sodium phosphateis about 50 g/L.

In the black layer stripping step: the volume concentration of thesulfuric acid is about 15 percent.

In the anodizing step: the mass concentration of the sulfuric acid isabout 180 g/L, and the additive is adipic acid with a mass concentrationof about 8 g/L.

In the sealing step: the mass concentration of the nickel acetate isabout 5 g/L.

Three samples of each group of the Al—Mg—Zn aluminum alloy workpiecescan be selected to test gloss and observe surface topography. The twodimensional surface topography of the samples can be observed under amicroscope at 40 times magnification, and the three dimensional surfacetopography of the samples can be observed under a 3D surface profiler.FIG. 4 and FIG. 5 illustrate the results of gloss test and theobservation of embodiment 1 through embodiment 9. Most of the glossvalues of the Al—Mg—Zn aluminum alloy workpieces processed by the methodof the embodiments of this disclosure are larger than 1300, and thelargest gloss value is 1422. FIG. 6 illustrate the results of gloss testand the observation of comparative embodiment 1 through embodiment 7.Most of the gloss values of the Al—Mg—Zn aluminum alloy workpiecesprocessed by the comparative embodiments are less than 1300, and thelargest gloss value is 1303.

As the surface topography of the samples in embodiment 1 to embodiment 9are similar, only a microphotograph of the sample processed by themethod of embodiment 1 is provided. A microphotograph of the sample ofcomparative embodiment 1 is also provided.

FIG. 7 illustrates that the there is no obvious bank mark or corrosionspot on the surface of the Al—Mg—Zn aluminum alloy workpiece processedby the method of embodiment 1 observed under microscope at 40 timesmagnification. FIG. 8 illustrates that there are obvious stripped bankmarks and white corrosion spots on the surface of the Al—Mg—Zn aluminumalloy workpiece processed by the method of comparative embodiment 1observed under microscope at 40 times magnification. FIG. 9 illustratesthat three dimensional surface of the Al—Mg—Zn aluminum alloy workpieceprocessed by the method of embodiment 1 is smooth. FIG. 10 illustratesthat three dimensional surface of the Al—Mg—Zn aluminum alloy workpieceprocessed by the method of the comparative embodiment 1 is rough. Theappearance of the Al—Mg—Zn aluminum alloy processed by the method ofembodiment can have no bank mark and have good gloss.

In the surface treating method for aluminum alloy having magnesium andzinc, the additive selected from a group consisting of adipic acid,1,2,3-Benzotriazole, oxalic acid, sodium malate and glycerin is added inthe anodizing solution. The additive can prevent preferentialdissolution of intermetallic compounds, thus the appearance of thealuminum alloy can be improved, and the gloss of the aluminum alloy canbe increased than conventional method.

The embodiments shown and described above are only examples. Manydetails are often found in the art such as the other features of methodsof surface treating and anodizing aluminum alloy workpiece and aanodizing solution. Therefore, many such details are neither shown nordescribed. Even though numerous characteristics and advantages of thepresent technology have been set forth in the foregoing description,together with details of the structure and function of the presentdisclosure, the disclosure is illustrative only, and changes may be madein the detail, comprising in matters of shape, size and arrangement ofthe parts within the principles of the present disclosure up to, andincluding the full extent established by the broad general meaning ofthe terms used in the claims. It will therefore be appreciated that theembodiments described above may be modified within the scope of theclaims.

What is claimed is:
 1. An anodizing solution for an aluminum alloy workpiece having zinc and magnesium, the anodizing solution comprising: a sulfuric acid with a mass concentration from about 150 g/L to 230 g/L; and an additive with a mass concentration from about 0.5 mg/L to 25 mg/L; wherein the additive comprises at least one compound selected from a group consisting of adipic acid, 1,2,3-Benzotriazole, oxalic acid, sodium malate, and glycerin.
 2. A method for anodizing an aluminum alloy workpiece having zinc and magnesium, the method comprising: anodizing the aluminum alloy workpiece using an anodizing solution, the anodizing solution comprising an acid solution and an additive with a mass concentration from about 0.5 mg/L to 25 mg/L; wherein the additive comprises at least one compound selected from a group consisting of adipic acid, 1,2,3-Benzotriazole, oxalic acid, sodium malate, and glycerin.
 3. The method as claimed in claim 2, wherein the acid solution is a sulfuric acid solution with a mass concentration from about 150 g/L to 230 g/L, a period of the anodizing process is from about 20 minutes to 50 minutes, a temperature of the anodizing process is from about 18 degrees Celsius to about 26 degrees Celsius, and a voltage of the anodizing process is from about 6 volts to about 10 volts.
 4. A method for surface treating an aluminum alloy workpiece having zinc and magnesium , the method comprising: supplying the aluminum alloy workpiece; polishing a surface of the aluminum alloy workpiece such that a surface of the aluminum alloy workpiece achieve a mirror effect; degreasing the aluminum alloy workpiece; anodizing the aluminum alloy to form an oxidation film on the surface of the aluminum alloy workpiece using an anodizing solution which comprising an acid solution and an additive with a mass concentration from about 0.5 mg/L to 25 mg/L, the additive comprising at least one compound selected from a group consisting of adipic acid, 1,2,3-Benzotriazole, oxalic acid, sodium malate, and glycerin; and sealing the aluminum alloy workpiece using a sealing solution.
 5. The method as claimed in claim 4, further comprising stripping a black film formed on the surface of the aluminum alloy workpiece after degreasing the aluminum alloy workpiece.
 6. The method as claimed in claim 5, wherein the black film is stripped using a sulfuric acid solution, a period of stripping the black film is in a range from about 20 seconds to 120 seconds, and a temperature of stripping the black film is room temperature.
 7. The method as claimed in claim 4, wherein the acid solution of anodizing the aluminum alloy workpiece is a sulfuric acid solution with a mass concentration from about 150 g/L to about 230 g/L, a period of anodizing is in a range from about 20 minutes to about 50 minutes, a temperature of anodizing is in a range from about 18 degrees Celsius to about 26 degrees Celsius, and a voltage of anodizing is in range from about 6 volts to about 10 volts.
 8. The method as claimed in claim 4, wherein a period of degreasing the aluminum alloy workpiece is in a range from about 3 minutes to 5 minutes, a temperature of degreasing is in a range from about 50 minutes to about 60 minutes, and a degreasing solution comprises sodium phosphate with a mass concentration of 40 g/L to 70 g/L.
 9. The method as claimed in claim 4, wherein a period of sealing the aluminum alloy workpiece is in a range from about 15 minutes to about 20 minutes, a temperature of the sealing is in a range from 90 degrees Celsius to about 95 degrees Celsius, and a sealing solution comprises nickel acetate with a mass concentration of 5 g/L to 10 g/L.
 10. The method as claimed in claim 4, wherein aluminum alloy is washed in water and dried after being sealed. 